Investigation On Effective Capacity For Multi-Relay Cooperative Communications With Limited Feedback

Because of the multipath fading in wireless network,the capacity of wireless communication system is greatly limited.Diversity technology can effectively overcome multipath fading and increases channel capacity without occupying additional bandwidth resources.Multi-antenna technology is a typical representative of diversity technology.But in practice,due to the limitation of power consumption and volume of user terminals,it is impossible to install too many antennas.Therefore,the relay cooperative communication technology emerges.Antenna sharing of the distributed relay,forming a virtual multi-antenna array,can effectively improve the physical layer transmission.This thesis mainly studies the key technologies to obtain a larger transmission capacity of the system in the case of limited channel state information(CSI)feedback.The main research work and innovations of this thesis are as follows:Firstly,the optimization of effective capacity in cooperative multi-relay communication network with limited feedback is studied,and a multi-relay precoding(MRP)scheme based on channel quantization error(CQE)is proposed.In this network,CSI is quantized,and CQE is considered when the destination node feeds back CSI to the relay.The use of more channel quantization bits can enhance the accuracy of quantized CSI obtained at the relay and increase the transmission capacity from relay to the destination.However,it also results in increased feedback overhead.The thesis defines the effective throughput as the difference between the transmission rate and the feedback rate in order to characterize the channel capacity after offsetting the feedback overhead.The simulation results show that the effective throughput of the proposed multi-relay precoding scheme oriented to channel quantization error(CQE-MRP)can be adjusted to obtain the maximum throughput of the communication system.Secondly,this thesis analyzes the performance of cooperative multi-relay communication networks with limited feedback.In order to study the performance of the system with limited feedback,a multi-relay beamforming scheme based channel quantization error(CQE-MRB)is proposed.According to the system model,a multi-relay cooperative beamforming vector is designed to maximize the transmission capacity of the system.The outage probability with CQE-MRB scheme is calculated and the reliability of the system is analyzed.Simulation results show that the proposed CQE-MRB scheme improves the outage performance of the system as the number of relays increases.In addition,the number of channel quantization bits can furtherminimize the outage probability of the proposed CQE-MRB scheme.Finally,the thesis studied the tradeoff between feedback overhead and reliability of multi-relay system based on threshold.In order to reduce the feedback overhead,the thesis propose a multi-relay selection scheme based on threshold.That is,relays which CSI over threshold are selected for beamforming and CSI feedback.By reducing the number of relays,feedback overhead of CSI is reduced.So,the system reliability must also decrease as the feedback overhead decreases.The thesis analyze the tradeoff between the feedback overhead and the system reliability with different threshold conditions,deduce the outage probability formula and the feedback overhead,and carry out the simulation analysis.The simulation results show that there is a tradeoff between the system reliability and feedback overhead with different threshold conditions.